Electron wave tube



Feb. 25, 1958 2,824,997

A. v. HAEFF ELECTRON WAVE 'TUBE Filed Oct. 14; 1949 6 Sheets-Sheet l CATHODE N92 ELECTRON BEAMS CATHODE N91 l4 FOCUSING I DRIFT TuqE SOLENOIDS OUTPUT INPUT OF LENGTH Z 5 2e GiRCUIT CIRCUIT ml fl II l I I l l 7-J VA cou.

SJ cl v INVENTOR ANDREW V. HAEFF Feb. 25, 1958 A. v. HAEFF ELECTRON WAVE TUBE 6 Sheets-Sheet 2 Filed Oct. 14, 1949 20 REAL AND IMAGINARY COMPONENTS OF PROPAGATION CONSTANT VS INHOMOGENEITY OF ELECTRON BEAM m E E REAL AND IMAGINARY COMPONENTS OF THE PROPAGATION CONSTANT VS AVERAGE m F TF m M A R V E N w v N o w R R T C D E N L E A ATTORNEYS Feb. 25, 1958 A. v. HAEFF 2,824,997

ELECTRON WAVE TUBE Filed Oct. 14, 1949 6 Sheets-Sheet 3 IN db IGNAL+ NOISE DRIFT POTENTIAL m UNITS OF it); I

GAIN VS DRIFT TUBE POTENTIAL FOR THE ELECTRON WAVE TUBE AT S/N= db IMAGINARY I =c|.mp/cm olz'sss'ra 9 4 IO DRIFT TUBE POTENTIAL IN UNITS OF[( 5] zrw, REAL AND IMAGINARY COMPONENTS OF PROPAGATION CONSTANT VS DRIFT TUBE POTENTIAL FOR TETRODE ELECTRON WAVE TUBE INVENTOR ANDREW V. HAEFF BYMU.

ATTORNEYS 1958 A. v. HAEFF 2,324,997

ELECTRON WAVE TUBE Filed Oct. 14, 1949 6 Sheets-Sheet 4 8 3 DRIFT TUBE POTENTIAL( 7 OUTPUT VS DRIFT TUBE POTENTIAL FOR TETRODE ELECTRON WAVE TUBE (Sl/NI=20db) E1515 SIGNAL+ NOISE 3/ ELECTRON WAVE TUBE OUTPUT NOISE. vs DRIFT TUBE POTENTIAL OUTPUT VS DRIFT TUBE POTENTIAL OF THE TWO-VELOCITY TYPE ELECTRON WAVE TUBE MIcRovdLTs OUTPUT I50 OHM (BEAM CURRENTSI I,= 4.5 MA., l =-9.5 MA.,V| -v so VOLTS) INVENTOR ANDREW V. HAEFF ATTORNEYS Feb. 25, 1958 A. V.,HAEFF 2,824,997

ELECTRON WAVE TUBE Filed Oct. 14, 1949 6 Sheets-Sheet 5 LIE-:LU

0000000 00000 OOOOOO 6 4 2 OUTPUT VS DRIFT INVENTOR AN DREW V. HAEFF ATTORNEYS 0 IO 20 -60 8O 9O IOO ELECTRONIC BANDWIDTH VS GAIN OF THE ELECTRON WAVE TUBE A. V. HAEF' F ELECTRON WAVE TUBE Feb. 25, 1958 6 Sheets-Sheet 6 Filed Oct. 14, 1949 MJ I IJH INVENTOR ANDREW V. HAEFF" ATTORNEYS United Sttes Faten t 2,824,997 w g- O WA E Andrew V. Haelf, Washington, D. Ar is i n Qst9ber 4,. ,9 Serial 9- 21, 35 .2 to 315- 6 (Gi antedn der Title 35, U, S. Code (1952), sec. 266) in ntion relat s to th s nsratipn an amp sat qn 9fsl tri9al si na b 1m afi9 of b ams o charged particles carrying the signals as space charge or velo ity variations and travelling at difierent average vei ities. The invention is particularly applicable in the field 9f very high radio frequencies in .wnicnampliiisai o and e at on of oscillat i ef c en or c ss'ib e w t pr quslylsn echn ques and pa a The operationof the present invention ,depends on energy transfer between beams of charged particles, travelwith difi'erent velocities, at least one of which carries a density or velocity modulation. The particles of the beams a're'in energy transferring relationship as they pass 9 .1 ea t s Thi ener t ans e m ifies a sp gha g s irge va i ti n ca e by Qns tn beam 'd ring its passage past the other beam. The space charge .mqdulaticn a m l fied ma n be rem ve t in the a. b syl ab 1i9 P i ss ss It is' aecprdingly the object of the present invention to may a o sep ate e ec ica s ls- M specific bb'feit of the i nvsnt e r t H m n appa a 'iq 't s P rp s n nov n i h o f ec in these ends.

Itw ould be preferred to describe the operation of .the present invention in quantitative physicalterms showing the transfer of the kinetic energy of the particles into the energy of the increasing space charge variation. Such computations, however, inherently are concerned with the h l /i9? 9? a a hos Pa ti l a e s b to a nverse s q uare law repulsion. hfinomena in snch a gas P' us Wall which ar no ne li b at emo nt fi iq in 1 9?! d in to he th o y f a erst i lis inv r ube n h h aws- T e h or of i is s ua e law a e a l beca s at th co i y r e d t ha o b en deve oped in la sica physics. i Consequently, rigorous mathematical treatment of the present invention cannot be given at the present time.

will later appear, restricted solutions fora number of gases have been efi ected which provide explanations 9f a nu mber of phenomena involved.

Accordingly, the invention will be described generally in physi calterms as an introduction to the specific em,-

bodiments thereof, and the mathematical treatment postponed to the end of the discussion.

' The amplification effects are produced by the interchange of energy between particles moving at different velocities, and the invention includes the cases where both beams are travelling in the same direction, particles in one overtaking the particles of the other, and also where the particles are travelling in opposite directions. While for convenience, two beams are referred to, more may be employed if desired.

In the operation of the invention energy is transferred from the faster to the slower particles during the transit of one particle past the other. Within this limitation, it has been found that space charge disturbances will be am- 2,824,997 Ce Patented Feb. 25, 1958 plified with many types of experimentalconditions soiar as the average and relative beam velocities are concerned and so far as the space charge density and currents of the beams are concerned. It ,is not to be inf rr d, hQ ever, that any arbitrary arrangement will amplify energy at any desired frequency. Not only is the electronic bandwidth of the apparatus of the presentir ven tion limited in dependency on the space charge density of the beams and their velocity distribution but within the operating frequencies there. exists a definite freqpencydor whichthe amplification is at its -In order to efiectthe desired energy transfer between the beams it is preferred that the beams traverse a common path. This offers little theoretical diflicnliies, since the statistical probability of collision'within the beams .pf practical current density is substantially l en-existent. Practically, interpenetrating electron bearnsare easily generated by two spiral filamentary cathodes or otherwise as will be apparent to those learned in the art.

The invention has'been'describedby the inventor in the Physical Review, vol. 14, p. 1532, and in The Proceedings ofthe institute of Radio- Engineers, vol. 37, No. 1, pp.

P10, and vol. 37, '7, p 778. These publications may be referred to for additional information.

Further explanation of the invention will be had in connection with the exemplary embodiments thereof shown in the drawings, in which:

Fig. 1 shows schematically an embodiment of the vention,

Fig. 2 shows acathode arrangement for the embpdiment'of Fig. 1,

Fig. 3 shows a second embodiment or" rhe invention,

Fig. 4 is a graphical showing the solutions of an equatiQfiHesCfibiHs e o erat n A FiQBS in t e in ertin Fi s 5 sho the o e ation of the tu 91": .F .1,

Figs. 7 and 8 show the operation of the tube off g Figs. 9 and 10 further show the operation of the tube Qi a d Fig. 11 shows the electronic band-width or" the tubes of the present invention.

Thesystem shown in Fig. 1 comprises a two beam tube for the amplification of electrical signals. This t be pomprises generally a pair of cathodes for generating a pair of interpenetrating beams of different velocities, a Kidd};- lator for applying an electrical signal to the eonipgsite beam to provide effective variations of its space charge e a dri be he in the s a ha e modulati is am d n t an d d lat h ou u citcuit for deriving the amplified energy frorn the no nppsite beam, and a collector electrode for receiving the beam from the out ut circuit.

Initially the beam is. generated by cathodes 1 and 2 whose heater elements are not shown in the drawings. As will be appreciated, the ,cathodesare insulated from one another in order that they may receive diiferent Operating P n i l forestablishing ahearn having two components of velocity. The beam is initiallyelectrostatically focused by the electrodes 3 and 4. These electrodes are returned to ground and the cathodes are supplied with negative potentials, cathode 1 being energized through voltage sources 5 and 6, and cathode '2 through sources 5 and 7. r

The beam then enters a region where it receiyes aspace charge modulation. Devices for modulating beamsin this manner are known, and may operate by modulating either the current or the velocity of the beam. The em; bodiment shown includes a grounded cylindrical electrode 10 containing a conductive helix 11, connected thereto at 12, whose other end is led as through a collar 13 to provide an input terminal at 14 for receiving the modulating signals. Velocity modulation is thus effected.

Were the signal applied directly to the electrode 1Q l the input signal frequency;

Duringtransit through plified space charge distribution.

' external.

in the absence of helix 11, current or charge density modulation would be obtained. For-this type of operation, of course, electrode would not be grounded for The modulated beam then enters 1a drift: space whose potentialis substantially? uniform and is determined by 1 h 1 2,824,995K A cathode 36 and grid 37 modulates the usual fashion. i i g I The modulated beam is focused by electrode;.46 energized at a; positive potential by voltage source 47. The beam is 'then'passed through drift tube 50 under the ifocusing action of solenoids 51 and 52. The' drift: tube}.

that ofcylindr'ical electrode l7l rThefoperating potential i of this electrode .with respect to :ground isprovided by potential source Puriug passages of the composite l beam through this tube as well as'through the'modula tor and demodulator, it is focused magnetically by splenoidslsand 19.1" f l V the drift tube the energy interchange between the t'wocornponejnts on the beam results 7 finan amplification are; spage chargevariation imposed by the modulator. The signal' level increases exponentially along the length of the drift tube.- While the conditions setting a maximum limit to the gain have not "been mathematically established, it is reasonable to presume, that some equilibrium condition would eventually be reached in which the energy of the space charge dis: 7 tribution becomes .constant and is not amplified during a' further transit in the drift space. i

- The tube of Figure'l is provided with a demodulator section 21 which receives the beam; on its emergence from the drift space and abstracts the energy ofthe ami i i This comprises cylindrical electrode 21. enclosing a conductive helix 22 which surrounds the beam and is' connected to 21 atone end, the other extending outwardly through collar 23 to form output'terrninall l. Thus, the outputcircuit is inductively coupled to the beam.

.A collectorelectrode 25 receivesthe beam from the V demodulator and is itself energized at a positive poten- 1 tial with relation to the cathode by'source 26.

The tube shown in Figured is of generally circular 'section and of'course is provided with an envelope for evacuation, to which solenoids 18 and 19 are: preferably A cathode arrangement for generating a composite beam is shown in Fig. 2, wherein two spiral filaments and Y 31 are supported in the same plane by :leads- 32.

As indicated, the 'leads rnay be positioned bypress 33 of the tube envelope. s i 7 7 n Theoperation of the invention as an oscillator is established by regenerative coupling between theoutput and potential is established by voltage source 53.

From the drift tube, the beam 'passes through another a focusing electrode 55 which isunaintained at the potential of voltage source 56. l

' prises a central collector electrode 57 and outer cylinder 58. The beam-enters the output circuit'throu'gh -grid- 59: 7 connected to the outer cylinder by annulus 61; The other end of the cylinder is capacitatively coupled to, electrode i 57 at ring.62 through annulus 63,. The potential of; the

collector relative to 'thegrid isdete'rmindfbY voltage 'sou'rce'65." The, output energy is clelivered'thro'ughci f cuit64. r 1 j r The shieldingaction of gr1d59 improves tlie efficiency of the, tube by redncing'the' etie'ctive transit time" of'lelec- 'trons received by thecollector 57," and consequently 'should be positioned near the latter; at a distanceshort relative to the physical wave-length'of the beam modula- 'tion; Since the signal is' amplified'in the drift tube before 'it arrives at the screen; the partition noise caused by'thei partial interception'of current by therscreen gridis negligible. In this respect the signal-to-noise'ratioapproaches: V that of the conventional triode. or i i W A s previously'mentioned,the tube'may' form an oscilt V lator where regenerative coupling is provided from {the 'loutput to the input." 7 j j *The provision of a single cathode in the construction ;of Fig. 3 causes the formation of whatsis' usually con 'sidered a single bear'n. The'electron :velocities of such a beamghowever, are, not uniform, .since the potential 'interiorly. of the beam section progressively decreases as the center thereof is approached, asa result of space charge fields. 'Components of differe'nt velocity are there? fore presentfor th e exchange ,of energy between faster 7 and slower electrons. s l v I The theory ofoperation of this tube is not fully understood at present, however, and the above factors may 'not constitute the entire explanation. The. amplification:

" is obtained at higherv averagejcurrent levels Qthanthe input circuits. In the circuit of Fig l, manifestly such coupling n provided from output lead 24 to input leadl4 i Typical operating voltages for the tube of Fig. 1 rela tive to ground, for a drift tube l0 inches long, at 3000. V

rnc /s. are as follows; i j a Thejtube jof Fig. 3 illustrates two main depairtures l a from that of Fig: l, which; may. be employeclseparate'ly las well as together. These features comprise the use of double. beam' tube ernploysQ and these levels approach half or rno re'of the. saturation current thatcan. be passed '7 through" the idrift tube under theoperating conditions.

Such saturation currentsforl various conditions are de r scribed by the inventor in'The Proceedings ofthe Insti- 'tute of Radio EngineersySe'ptembe'r'1939," pp.;586-602.

Typical'operatingvoltages.for the tube of'Figl 3Iwith a 20 cm, drift tube, SVmaQbeamfcurrent at 3000 mc'./s.,. would be a negative grid bias of 5lvolts, first focusing electrode 200 volts; drift tube 120 volts', second focusing electrode andlscreen g d.. 20.0 v0l t's, and thencollector electrode 150 volts, all relativeto'cafhQdeQ- V 1 T he structural "differences betweenlfigsil andj should asingle cathode to generategthebeam, and the use of a i screen to establish tetrode operating conditions in the tuber In'Fig; 3 the indirectly 'heated cathode'consists of a r cylinder35 with an emitting end face 36. j Current modu-' Y7 lation isobtained by potential variations of grid 37,

caused by operationrof'a resonant input circuit formed not obscure thefact that th' ejqmethods of. operatiodmay be varied as desired. "Ilius, the tutielofglfig.; 1' ma be operated as a single cathode tube whiereflthe two. cath? 'ode'sare held at the same 'potentialn ..The tubeIof'Fig.3

' may be empro d 'asudfibikgthoa tube hereithe l by cathodemember35 and a cylinder 38 coaxial there-x with; Annulus 'C0l1I1 ClZSfth"grld.tO one end of cylinder 38, whose'other end is coupled to'the center conductor by;annulus.41 and coupling ring 42. The resonant structure is excited'by an input circuit 43. The desired biasin g potential is provided by voltage source .45. The voltagerrvariation at thesignal frequency between the grid 37 is biased p osi'tive"of thecathode 3 3 so as to draw current and be'heated to emissionternperatures. isecpngh ary emission from the positive grid also may-b661 ployed for a second sa ce of-electrons. Whilesthe:

structure bfFigJLWould beiprefer ifed for the latter' type' of operation, the main principles: involved: are si bsts 'tially the samezr'zr' a. if i V .j Having described the exernpla'rv embodiments oftth;

invention, the operating' 'theory will' be' considered 'ih' mh; i

" When a high temperature is placedclose to alow'i temperature body the heat' energy flows in the direction which .tends to equalize "the temperatures -.of the two bodies in contact. This is one case :of asgeneral law rof statistics that the ventropy tends to increase. if an electron stream of high energy is projected in the proximity of another electronstream of lowerenergy, then, by .the mechanism of elastic collisions between 'fast and slow electrons, there will be a gradual interchange of'energy between the two streams with the result that on the average, the fast electrons are'slowed down and the slow ones are speeded up. The nature of this process is similar to e'lastic scatterin'gmf hig'h energy partic'les by 'other;particles which are either stationary-or moving -s lowly. In the-case of electron scattering, the forces acting between the-electrons obey Coulombs law. As'aconsequencethe mechanism ofscattering of electrons by-e'lectrons can be described in terms :of the lfamiliar concepts of electromagnetic theory.

Consider a .uniform stream ot electrons-of charge-density p moving in the Z-direction with the velocity v;. Any disturbance of the :stream =will produce electron waves in the stream. By electron waves is meant either space-charge density fluctuations with associated electric field fluctuations, orvelocity fluctuations of electronsin the stream. Thepphase velocity of itheseawavesfidepencls upon the space-charge-density. .Two waves .arehsually associated withanydisturbance. Onelof these waves has its ;.phase velocity somewhat'higherthan the velocity :of translationof electrons in the stream .and .the other wave has velocity:lower'than the'translational velocity.

11f --another stream of electrons of density :p -:moving with velocity v is injected near'or .intolthe space "occu pied by the first electron stream, the electron waves interactso that the phase velocitiesdfselectronwaves in the :twostreams are modified and an.inter-change='of e'nergybetween the *two streams takes fplace. 'It is-most convenient for the purposes of analysis-to.considerzthe two :streams ofelectrons as components of one-inhomogeneousfstream. The space-charge densities p, 'current Inthese expressions-the first symbol representsaverage-or D. C. quantities and the second symbol represents first order quantities whichacan be assumed to'vacy1zwith time 'and distance in-anexponential manner similarcto variationsof the voltage V:

, V FZ+iwl 4 where'I'is the propagation constant, w is the frequency ofithe disturbance, or signal, having an initial value Y at 2:0. 7 7

The fundamental equations whichare requiredi'n the analysis are: (a) Poissons equation:

(b)l'The equation expressing conservation .of electric charge:

By using Relations 3 in the Formula ,6 we obtain:

it e-b51221) 'j a= (52 a'- 2P) Solving. for V; and 1:12,, we get:

apfiow rva (9) Substituting (9) into (7) i 2= 3 ow v1) IV 5 2;. ow v2) Solving for E and E two electron streams, andthe corresponding space-charge densities p and p Excluding :trivial solutions :correspondin-g :ito conditions: that either I=O or V=0 and replacing spacc-charge-dem sities by electron plasma frequencies W and w from defining expressions:

we obtain the equation from which-the propagation constant of the inhomogeneous stream canbe obtained:

1 "z e +J 1) (w+.1 z) V 7 It can be easily shown that in ageneralcas'e ,ofiacoma posite'stream of electrons having many ,compriuentsot plasma frequencies w, and velocities v, theformula takes the form: i

' can be written as follows tron plasma frequently;

are s'hown plottedrinFignre as a function of V homogeneity ew/ywt 'of -ithe election stream. The real V cornponent has finite vaine bnly o'vera limited range of r the inhomogeneity factor; fromQO to al value ota/2i; It

locities between the lirn'its of v gwdwi" 1 1- dv t e w'irrvr H Inthe case' of a homogeneous electron beam when 19 the Formula 14 reduces to a familiar form:

"peanutvar: 15 The solution of'Equatipnfi immediately gives the familiar expression for :the propagation constant:

g-QI': V I 7' r1 n] wi V The Expression 16 shows that two electron wavesprdp agate along the beam with the velocities somewhat higher 7 a 'and somewhatjlower than theaverag'e electron velocity. i These waves produce interference-etfects inthe beam which manifest themselves. by the fact that'along the' beam periodic conversion of kinetic energy oielectrons 'In order to solve the Equation 14in thecase when the velocities are not equal we can tassumethat;

a where v is the average'velocity of electrons 'in the stream,

'and 26 represents the difference streams; i. e., 26 =v 'v In terms trand th e F o rmula isen 1: be written asig ingformz 7 The factor ew/vwf i dimensionless andexpressesitlie degree of inhomogeneity of the electron stream; the'q'uantity' 511 W isjpr' ophrtionafto:itherlookeiiifor component of s the propagation, constan ponents of the normalized pr'd agsaa aasi afjm x 2 z l 0) '51: This equation "can be solved explicitly for .gaicas when In this case the equation reduces to the follbw- Again, in the case o-fr .a continuous distribution of veand v the Formula 14' the. propagation constant with frequency, The ratio of,

the square of the amplitude of thejdisturba'n'ce at a.dis- I V i tance Z-along the beam to'th e magnitude of the disturbance at its origin"at"Z .'0, represents a gain in energyof the exponentially withithe'lengthZJ' W a ,The general solution tofEguationl4 hasbeen' obtained in;ve'locity of the two 7 by standard methdds.;- The,solutions defining conditions, T r l 1 for amplification areshown in" Fig. .12, wherelthenor- ;is' only over 'thi s range that efi amplification'of: the

disturbances can take placef The maximum value of the real component is equal to one-half when the 'inhomo-v geneity is equal to thevalue of 3 /2.mIhe,formu1 ex pressing the amplitude ofthe'disturbance-in-thiscaselis as follows: i

9f the propagation constant. e w r V a a 7 T e. alue o t ma a y p nen of the m nag r.

where 'y is the real, and-'9 is theeimaginar y component Since the inhomogeneity of the; beamji's proportional totheisignalfrequency, thecurves of Figure 4 alsojrepre sent variations of' the real and imaginary components of disturbance; For large jvalue-o'f he gain increases malized realtcomponent of? the propagation constant,

' geneity iactory-fx1for t-difierentrvaluesnof a distribution tiijals" betwe en" cathode 1; {cathode 7 7 a are? adjusted so jthat the inhomogene tyfactor approac i plasma'frequency'ythe the value of current densityrinthe beamf Sincethe mum value of the norrnaliaed jreal compo enti'of -t'he factor p. The generalinhomogeneityffactorcorresponds,-v t to that mentioned above'ifi the geometricmeanivaluesrofg velocity and plasma frequently, are usedin the expression 1 defining'the homogeneityfactor;4hsis( g w /v wifi g;v a The'curves rise to a 'rnaximurnvalue of,.5 fort- 2:2, '(h =l); the maxima'for. the'other'curves are lower,*butf the maxima do not fall of? particularly rapidly as p increases. Consequently,. the tubesof the presentfinvention 7 i will produceamplificationrover a wider; range of inhomoe geneity factor as p increases;

and focusing electrodes placed infrontof thefcathodes project the'electron streams'through along, h'QIlOW metaI-f 1 cylinder, usually called theidrift tube.-- Atethe opposite a end of the tube the electrons are collected by a collector a 1 t "electrode The divergence of the electron'strearn; islprer vented by the use of magneticifield parallelto thelvelocity of relectrons in the strearnfl Thisgfield ispreatedby focus 1 Y 7 ing solenoids as shownfin thfe'fignre. Thelinprits'igital "s brought 1.0711716 i p t n ic he uh by means; of a trans:

mission line which terminates in a shorthelixjsurrounding the electron stream." In

putci u t'a a hown i In order to obtainim aggin1prngain uistment d epends'upo :The tube of Fig; l ptilizes aninhomogeneouselectron '7 I p e is manner the sig nal voltage produces initial disturbance in' the ,rbeamr 'This'jdis' e turban'ce is amplified in: an:exponential nianner alon'g th 7 length of the drift tube; Greatly amplified fluctuations in" t the eleetro'nstream induce YOltagesinthje output'circuiti 1 This circuit can be simi l inthe figure;

propagation constant is equal to 0.5, the maximum gain of the electron wave tube can be expressed as:

cm.(amp./em.

volts 3/4 (25) Instead of adjustment of the difference of potential between the two cathodes, the drift tube potential can be adjusted for optimum gain. For a constant current in the beam the variation of the real and imaginary components of the propagation constant with the potential of the drift tube expressed in dimensionless units is shown in Figure 5. The real component reaches its maximum value at the normalized drift tube voltage of approximately 0.4. The variation of the output, or gain of the tube with the drift tube potential can be easily derived from the' generalized curves of Figure 4. Such a diagram is represented in Figure 6 where a rapid increase in gain as the voltage is lowered can be readily seen. The efiect of interference of the component waves 'is apparent in the fluctuations of the output as the drift voltage is varied.

In the tube of Fig. 3, only one electron beam is used. in this case the inhomogeneity of the beam is the result of the space-charge reduction of the potential along the axis of the beam so that outer electrons travel at a velocity higher than the velocity of electrons along the axis. The variation of the real and imaginary components of the propagation constant with the drift tube voltage for this space-charge type of electron wave tube, is shown in Figure 7. In general, the shape of the curves in this figure resemble very much those of Figure 5. The variation of the output with the drift tube voltage for space-charge type tube is shown in Figure 8.

Experimental curves of Figures 9 and 10 show variation of output with the drift tube potential. A close resemblance, in most respects, to the theoretical curves of Figure 8 is apparent. These experimental data were obtained for the drift tube 20 centimeters in length.

The generalized curves of Figure 4 make it possible to estimate the electronic bandwidth of the electron wave tube. The variation of the fractional bandwidth with the gain of the tube is shown in Figure 11. It is interesting to observe that at gains as high as 100 decibels, the electronic bandwidth is still greater than 30 percent.

It will be understood that the embodiments described above are not to be taken as limiting, but as exemplary preferred constructions and techniques for illustrating the practice of the present invention.

The invention described herein may be manufactured and used by or for the Government of the United States 10 of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. A signal amplifying device comprising shield means establishing a beam transmitting path of uniform potential along an extended portion of its length, a single cathode gun means positioned to inject an inhomogeneous beam of charged particles at different velocities into said shield means, said gun means having a single emitting surface and adapted to produce a single beam of said particles having a relatively large cross-sectional area, beam modulating means positioned between said gun means and said shield means operative to modulate beam particles at a high signal frequency, said gun means being adjustable to supply an average beam current which is a fraction not less than about half of the maximum beam current transmissible through the shield means transmitting path, and beam modulation responsive means operative at the signal frequency positioned to receive the modulated beam particles after passage through the beam transmitting path.

2. A signal amplifying device comprising shield means establishing a beam transmitting path of uniform potential along an extended portion of its length, a single cathode gun means positioned to inject an inhomogeneous beam of charged particles at different velocities into said shield means, said gun means having a single emitting surface and adapted to produce a single beam of said particles having a relatively large cross-sectional area, resonant chamber modulating means encompassing at least said emitting surface of said particle gun means and operative to modulate beam particles at a high signal frequency, said gun means being adjustable to supply an average beam current which is a fraction not less than about half of the maximum beam current transmissible through the shield means transmitting path, and beam modulation responsive means operative at the signal frequency positioned to receive the modulated beam particles after passage through the beam transmitting path.

References Cited in the file of this patent UNITED STATES PATENTS 2,367,295 Llewellyn Jan. 16, 1945 2,406,370 Hansen et al. Aug. 27, 1946 2,541,843 Tiley Feb. 13, 1951 2,652,513 Hollenberg Sept. 15, 1953 FOREIGN PATENTS 934,220 France Jan. 7, 1948 OTHER REFERENCES Electronics, November 1946, pp. -92. Article by A. V. Hollenberg, pp. 52-58, incl., Bell System Tech. Jour., January 1949. 

